1. Field of the Invention
The present invention relates to a semiconductor photonic device, and more particularly to a semiconductor photonic device having a GaN-based compound semiconductor layer as an active layer.
2. Description of the Related Art
As materials for semiconductor photonic devices, such as a light emitting diode (LED), a laser diode (LD), and the like which emit blue light or ultraviolet rays, known are Group III-V compound semiconductors which have a general formula of InxGayAlzN where x+y+z=1, 0xe2x89xa6xxe2x89xa61, 0xe2x89xa6yxe2x89xa61, and 0xe2x89xa6zxe2x89xa61. The compound semiconductors are collectively referred to as GaN-based compound semiconductors. Since the GaN-based compound semiconductors are of a direct transition type, photonic devices using the GaN-based compound semiconductors have a high light emitting efficiency, and their light emitting wave lengths can be easily controlled with the concentration of In. Accordingly, as a light emitting element material, great attention has been attracted to the compound semiconductors.
In spite of the promising feature of the photonic devices using the GaN-based compound semiconductors, such photonic devices are still difficult to be realized for practical use. This is because it is very difficult to produce a single crystal of the GaN-based compound semiconductors having a large diameter.
In order to solve the problem, employed is a so-called hetero-epitaxial growth method by which the single crystal of the GaN-based compound semiconductor is grown on a substrate made of a material different from the GaN-based compound semiconductor. In addition, it has been proposed to use a ZnO layer as a buffer layer between the substrate and the GaN-based semiconductor layer to be grown on the substrate.
For example, Japanese Unexamined Patent Publication No. 9-45960 discloses semiconductor light-emitting device in which a ZnO layer doped with Al is provided between an InGaAlN layer and a silicon substrate. Japanese Unexamined Patent Publication No. 9-296936 discloses a laser diode in which a ZnO layer doped with Al is provided between a sapphire substrate and GaN layer. In these devices, the ZnO layer is doped with Al so that the ZnO layer has a conductivity.
Although it is stated in these documents that these devices have an improved long life time, it is found by the inventor that these devices suffer from the problem that the light-emitting characteristics and physical properties gradually change during operation.
The present invention is directed to a photonic device that can solve the aforementioned problem. The semiconductor photonic device comprises: a substrate; a ZnO buffer layer provided on the substrate; and an InxGayAlzN compound semiconductor layer provided on the ZnO layer, where x+y+z=1, 0xe2x89xa6xxe2x89xa61, 0xe2x89xa6yxe2x89xa61, 0xe2x89xa6zxe2x89xa61, and wherein the ZnO buffer layer excludes, as a constituent element, an element of the InxGayAlzN compound semiconductor.
The ZnO buffer layer preferably excludes Al, In and Ga and is doped with at least one element selected from the group consisting of B, Sc, Y, La, Ac, Tl, V, Nb, Ta, P, As, Sb and Bi.
The ZnO buffer layer has preferably a specific resistance of 10 xcexa9xc2x7cm or less.
For the purpose of illustrating the invention, there is shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.